In the 1980’s NZ developed a world leading fisheries management system. It was based on the idea of sustainable harvesting.

Questions

Why do you think there was a need to control harvesting from the sea?

In land based harvesting we tend to exploit the grazers (sheep and cows rather than tigers and wolves) What is it about the way we harvest from the marine ecosystem that can be a problem?

Trophic cascadesSome other clear examples of strong top-down control are seen in the marine environment. In the Pacific Coast of North America there are “kelp forests” of very large brown algae. These are grazed by sea urchins, which are, in turn, eaten by sea otters. When sea otter populations are reduced (as they were a century ago because of hunting, and again lately due to killer whale predation) the sea urchin populations can grow out of control and graze down most the kelp, creating “urchin barrens.” Unchecked by otters, they can bloom and basically destroy the kelp forest by eating huge amounts of kelp. When population control of prey by their predators (as in the sea otter/sea urchin interaction below) then affects the next level down, the kelp, it is referred to as a “trophic cascade.” http://www.eoearth.org/view/article/156656/

Now read this article and compare the situation described above (where otters are the keystone species) to what can happen in the NZ marine environment.

QuestionsWhat is the keystone species in the NZ ecosystem, what has happened to that population?

But is there another side to the story? Read the this article. So what is really going on? How can we find out?